Copyright 1997 ViaDSP, Inc. A portion of the disclosure of this patent document contains material which is subject to copyright protection. The copyright owner has no objection to reproduction by anyone of the patent document or the patent disclosure, as it appears in the U.S. Patent and Trademark Office patent file or records, but otherwise reserves all copyright rights whatsoever.
The present invention relates generally to an apparatus and method for providing communication between modems over digital networks, and more specifically, the present invention is directed to methods and apparatus for providing high speed modem relay using locally connecting modems.
A number of standards exist for defining communication protocols between modems coupled together for communication over the Public Switched Telephone Network (PSTN) or for communication over dedicated lines. For example, these standards include the V.34, V.32, and V.32bis standards among other standards promulgated by the International Telecommunications Union (ITU). A number of problems arise when modems implementing one of the above standards, or some similar standard, are coupled together over a digital link as shown in FIG. 1 and described below.
FIG. 1 shows a communication system 10 for providing full-duplex communication between modems 12 and 14. The communication system includes, in addition to modems 12 and 14, a first PSTN 16, a second PSTN 18, a first switch 20, a second switch 22, and a digital channel 24 connecting the first switch to the second switch. As understood by those skilled in the art, either or both of the PSTNs 16 and 18 could be replaced by dedicated lines. The digital channel may be implemented in one of a number of different ways such as through packet switched or synchronous transmission networks examples of which are the internet and a private satellite network respectively. Each of the first switch 20 and the second switch 22 includes a modem, which may be similar to modems 12 and 14. The use of the modems in the switches minimizes the bandwidth needed to pass data over the digital network. In addition, each of the switches includes circuitry for coupling to the digital channel 24.
Several problems arise when attempting to use standard high-speed modems as the modems 12 and 14 in the communication system 10. These problems are due primarily to the relatively long network dependent propagation delays between switches 20 and 22, which make it difficult for the system to support features of high speed modems defined in the V.34 and V.32bis standards. These features include: automoding, a feature which allows a high-speed modem, to recognize and communicate with a xe2x80x9cslowerxe2x80x9d modem such as a V.22 or V.22bis modem; and xe2x80x9ctrainingxe2x80x9d, including retraining, and xe2x80x9crate negotiationxe2x80x9d, including renegotiation, which allow connected modems to train their equalizers and dynamically alter the data rate between the modems (while in data phase) based on continuous analysis of line conditions.
Another problem that can arise when using high speed modems in the communication system 10 is that differences in clock speeds may result in unacceptable bit error rates. For example, typical modem standards require that the clock offset of the clock signal used to transmit data be less than xc2x10.01% of the baud rate. If in the system 10, the clock rate for sending data from modem 12 is 0.01% faster than nominal and the corresponding clock rate within switch 22 is 0.01% slower than nominal, then there will be a periodic inherent data loss in the communication system. In some prior art systems, this clock problem is hidden by error correction protocols negotiated by the end modems 12 and 14 that enable retransmission of lost data. This solution, however, results in an undesirable reduction in the effective data rate between modem 12 and modem 14.
Embodiments of the present invention provide methods and apparatus that overcome the problems and drawbacks discussed above associated with operating modems over digital channels.
In one general aspect, the invention features an apparatus used in a system for providing communication over a digital channel to couple a first modem on a first network to a second modem on a second network. The apparatus includes a modem module that couples to the first modem over the first network. The modem module provides data to the first modem at a data rate determined in part by a modulation rate of the modem module. The apparatus further includes a digital channel interface module coupled to the modem module, the digital channel interface module including a buffer that receives data from the digital channel and provides data to the modem module, and a control circuit coupled to the buffer and the modem module, the control circuit being constructed and arranged to detect a level of data in the buffer and to modify the modulation rate of the modem module based on the level of data detected.
The digital channel can be coupled to a second apparatus, and the digital channel interface module can be constructed and arranged to communicate with the second apparatus over the digital channel. The modem module can be adapted to receive automoding signals from the first modem and to transfer the automoding signals to the digital channel interface module, and the digital channel interface module can be adapted to send data corresponding to the automoding signals to the second apparatus over the digital channel. The digital channel interface module can be adapted to receive automoding signals from the other apparatus over the digital channel and to transfer the automoding signals to the modem interface module, and the modem interface module can be adapted to send data corresponding to the automoding signals to the first modem. The modem interface module can be adapted to receive rate renegotiation signals from the first modem and to transfer the rate renegotiation signals to the digital channel interface module, and the digital channel interface module can be adapted to send data corresponding to the rate renegotiation signals to the second apparatus over the digital channel. The digital channel interface module can be adapted to receive rate renegotiation signals from the other apparatus over the digital channel and to transfer the rate renegotiation signals to the modem interface module, and the modem interface module can be adapted to send data corresponding to the rate renegotiation signals to the first modem. The first network can be a public switched telephone network, and the modem interface module can be constructed and arranged to communicate with the first modem over the public switched telephone network. The modem interface module can include modems of the type defined by V.34, V.32 and V.22 families of ITU specifications.
A second aspect of the present invention is directed to an apparatus used in a system for providing communication over a digital channel to couple a first modem on a first network to a second modem on a second network. The apparatus includes first means for operatively coupling to the first modem over the first network to provide a data signal having a data modulation rate to the first modem, second means for transmitting data to and for receiving data from the digital channel, data storage means for storing data received from the digital channel, and control means, coupled to the first means, the second means and the data storage means, for detecting a level of data in the data storage means and for modifying the modulation rate based on the level of data detected.
The first means can include means for receiving automoding signals from the first modem, and means for transferring the automoding signals to the second means, and the second means can include means for sending data corresponding to the automoding signals to a second apparatus over the digital channel. The second means can include means for receiving automoding signals from the second apparatus over the digital channel and means for transferring the automoding signals to the first means, and the first means can include means for sending data corresponding to the automoding signals to the first modem. The first means can include means for receiving rate renegotiation signals from the first modem and means for transferring the rate renegotiation signals to the second means, and the second means can include means for sending data corresponding to the rate renegotiation signals to the second apparatus over the digital channel. The second means can include means for receiving rate renegotiation signals from the second apparatus over the digital channel and means for transferring the rate renegotiation signals to the first means, and the first means can include means for sending data corresponding to the rate renegotiation signals to the first modem.
A third aspect of the present invention is directed to an apparatus used in a system for providing communication over a digital channel to couple a first modem on a first network to a second modem on a second network. The apparatus includes first means for operatively coupling to the first modem over the first network to provide a data signal having a data modulation rate to the first modem, second means for transmitting data to and for receiving data from the digital channel, and control means, coupled to the first means, the second means and the data storage means, for controlling operation of the apparatus. The first means includes means for receiving automoding signals from the first modem, and means for transferring the automoding signals to the second means, and the second means includes means for sending data corresponding to the automoding signals to a second apparatus over the digital channel.
The second means of the third apparatus can include means for receiving automoding signals from the second apparatus over the digital channel and means for transferring the automoding signals to the first means, and the first means includes means for sending data corresponding to the automoding signals to the first modem. The first means can include means for receiving rate renegotiation signals from the first modem and means for transferring the rate renegotiation signals to the second means, and the second means can include means for sending data corresponding to the rate renegotiation signals to a second apparatus over the digital channel. The second means can include means for receiving rate renegotiation signals from the second apparatus over the digital channel and means for transferring the rate renegotiation signals to the first means, and the first means can include means for sending data corresponding to the rate renegotiation signals to the first modem.
A fourth aspect of the present invention is directed to an apparatus used in a system for providing communication over a digital channel to couple a first modem on a first network to a second modem on a second network. The apparatus of the fourth aspect includes first means for operatively coupling to the first modem over the first network to provide a data signal having a data modulation rate to the first modem, second means for transmitting data to and for receiving data from the digital channel, and control means, coupled to the first means, the second means and the data storage means, for controlling operation of the apparatus. The first means includes means for receiving rate renegotiation signals from the first modem and means for transferring the rate renegotiation signals to the second means, and the second means includes means for sending data corresponding to the rate renegotiation signals to a second apparatus over the digital channel.
The second means can include means for receiving rate renegotiation signals from the second apparatus over the digital channel and means for transferring the rate renegotiation signals to the first means, and the first means can include means for sending data corresponding to the rate renegotiation signals to the first modem.
A fifth aspect of the present invention is directed to a method for transmitting data between a first modem and a second modem over a digital channel using first and second switches coupled to the digital channel. The method includes steps of establishing a first connection between the first modem and the first switch, establishing a second connection between the second modem and the second switch, transmitting data from the first modem to the second modem through the first switch, the digital channel and the second switch, monitoring a level of data in a buffer in the second switch, and varying a modulation rate of data transmitted from the second switch to the second modem based on the level of data detected in the buffer.
A sixth aspect of the present invention is directed to a method for establishing data transmission between a first modem and a second modem over a transmission path that includes a first switch, a second switch, a digital channel coupled between the first switch and the second switch, a first network coupled between the first modem and the first switch and a second network coupled between the second switch and the second modem. The method includes steps of transmitting a first automoding signal in accordance with a predefined protocol from the second modem to the second switch, transmitting a signal representative of the first automoding signal from the second switch to the first switch over the digital channel, and transmitting the first automoding signal from the first switch to the first modem. The first automoding signal includes data representative of data transmission modes supported by the second modem.
The method can further include a step of transmitting a second automoding signal from the first modem to the first switch, wherein the second automoding signal includes data representative of data transmission modes supported by the first modem. The method can further include a step of transmitting data between the first modem and the second modem over the transmission path using a data transmission mode identified by both the first automoding signal and the second automoding signal. The method can further include steps of transmitting a first rate renegotiation signal from the first modem to the second modem over the transmission path, and performing a rate renegotiation process to establish a transmission data rate for data transmission between the first modem and the second modem.